I cant select only one active object in blender
Your objects are probably linked to each other, so when you change one of them you change the others too



If you select one  of those objects you should see in the object data tab that near the mesh name there is a 2 or another number: that means that there are 2 (or more) objects that share that mesh.

To solve it, click on that "2" button or in the 3d viewport choose Object>Relations>Make Single User> Object and Data